import java.util.Scanner;

public class Main1957 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int b = sc.nextInt();
        int c = sc.nextInt();
        double x = (a + b + c) / 3.0;
        System.out.println(String.format("%.3f",x));
    }
}
